This annual shareholder report contains important information about iShares Short-Term TIPS Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Shares	$11	0.11%

Expenses Paid, Amount

$ 11

Expense Ratio, Percent

0.11%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Institutional Shares returned 4.72%.
For the same period, the ICE BofA US Broad Market Index returned 1.47% and the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L) returned 4.69%.

What contributed to performance?

The principal value for TIPS is indexed to inflation, meaning that the principal value is adjusted higher every six months as inflation rises and vice versa. In addition, the stated yield applies to the adjusted principal value. As such, TIPS trade higher when investors expect inflation to rise and trade lower when the opposite is the case. Returns for TIPS are also influenced by the direction of nominal Treasury yields. During the period, prices for short-term TIPS were supported by relatively stable inflation expectations while the rise in nominal Treasury yields had less of a negative impact on shorter maturity TIPS. As a result, the benchmark finished with a meaningful positive return.

What detracted from performance?

There were no detractors from absolute performance.

The views expressed reflect the opinions of BlackRock as of the date of this report and are subject to change based on changes in market, economic or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: February 16, 2016 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		Since Fund Inception
Institutional Shares	4.72	%	3.23	%	2.78	%
ICE BofA US Broad Market Index	1.47		(0.34	)	1.26
Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L)	4.69		3.34		2.88

Performance Inception Date

Feb. 16, 2016

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 452,665,507

Holdings Count | Holding

Advisory Fees Paid, Amount

$ 0

Investment Company Portfolio Turnover

18.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$452,665,507
Number of Portfolio Holdings	28
Net Investment Advisory Fees	$0
Portfolio Turnover Rate	18%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Maturity allocation
Period	Percent of Total Investments^(a)
1-2 Years	22.7	%
2-3 Years	24.1	%
3-4 Years	26.8	%
4-5 Years	26.4	%

Five largest holdings
Security	Percent of Total Investments^(a)
U.S. Treasury Inflation-Indexed Notes, 2.13%, 04/15/29	5.2	%
U.S. Treasury Inflation-Indexed Notes, 2.38%, 10/15/28	5.0	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/29	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/27	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.25%, 04/15/28	4.7	%

^(a)	Excludes short-term securities.

Largest Holdings [Text Block]

Five largest holdings
Security	Percent of Total Investments^(a)
U.S. Treasury Inflation-Indexed Notes, 2.13%, 04/15/29	5.2	%
U.S. Treasury Inflation-Indexed Notes, 2.38%, 10/15/28	5.0	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/29	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/27	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.25%, 04/15/28	4.7	%

^(a)	Excludes short-term securities.

C000166148 [Member]

Shareholder Report [Line Items]

Fund Name

iShares Short-Term TIPS Bond Index Fund

Class Name

Investor A Shares

Trading Symbol

BAIPX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about iShares Short-Term TIPS Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Investor A Shares	$37	0.36%

Expenses Paid, Amount

$ 37

Expense Ratio, Percent

0.36%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Investor A Shares returned 4.45%.
For the same period, the ICE BofA US Broad Market Index returned 1.47% and the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L) returned 4.69%.

What contributed to performance?

What detracted from performance?

There were no detractors from absolute performance.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: February 16, 2016 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		Since Fund Inception
Investor A Shares	4.45	%	2.96	%	2.51	%
ICE BofA US Broad Market Index	1.47		(0.34	)	1.26
Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L)	4.69		3.34		2.88

Performance Inception Date

Feb. 16, 2016

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 452,665,507

Holdings Count | Holding

Advisory Fees Paid, Amount

$ 0

Investment Company Portfolio Turnover

18.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$452,665,507
Number of Portfolio Holdings	28
Net Investment Advisory Fees	$0
Portfolio Turnover Rate	18%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Maturity allocation
Period	Percent of Total Investments^(a)
1-2 Years	22.7	%
2-3 Years	24.1	%
3-4 Years	26.8	%
4-5 Years	26.4	%

Five largest holdings
Security	Percent of Total Investments^(a)
U.S. Treasury Inflation-Indexed Notes, 2.13%, 04/15/29	5.2	%
U.S. Treasury Inflation-Indexed Notes, 2.38%, 10/15/28	5.0	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/29	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/27	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.25%, 04/15/28	4.7	%

^(a)	Excludes short-term securities.

Largest Holdings [Text Block]

Five largest holdings
Security	Percent of Total Investments^(a)
U.S. Treasury Inflation-Indexed Notes, 2.13%, 04/15/29	5.2	%
U.S. Treasury Inflation-Indexed Notes, 2.38%, 10/15/28	5.0	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/29	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/27	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.25%, 04/15/28	4.7	%

^(a)	Excludes short-term securities.

C000166150 [Member]

Shareholder Report [Line Items]

Fund Name

iShares Short-Term TIPS Bond Index Fund

Class Name

Class K Shares

Trading Symbol

BKIPX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about iShares Short-Term TIPS Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class K Shares	$6	0.06%

Expenses Paid, Amount

$ 6

Expense Ratio, Percent

0.06%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Class K Shares returned 4.77%.
For the same period, the ICE BofA US Broad Market Index returned 1.47% and the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L) returned 4.69%.

What contributed to performance?

What detracted from performance?

There were no detractors from absolute performance.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: February 16, 2016 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		Since Fund Inception
Class K Shares	4.77	%	3.25	%	2.81	%
ICE BofA US Broad Market Index	1.47		(0.34	)	1.26
Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L)	4.69		3.34		2.88

Performance Inception Date

Feb. 16, 2016

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 452,665,507

Holdings Count | Holding

Advisory Fees Paid, Amount

$ 0

Investment Company Portfolio Turnover

18.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$452,665,507
Number of Portfolio Holdings	28
Net Investment Advisory Fees	$0
Portfolio Turnover Rate	18%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Maturity allocation
Period	Percent of Total Investments^(a)
1-2 Years	22.7	%
2-3 Years	24.1	%
3-4 Years	26.8	%
4-5 Years	26.4	%

Five largest holdings
Security	Percent of Total Investments^(a)
U.S. Treasury Inflation-Indexed Notes, 2.13%, 04/15/29	5.2	%
U.S. Treasury Inflation-Indexed Notes, 2.38%, 10/15/28	5.0	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/29	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/27	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.25%, 04/15/28	4.7	%

^(a)	Excludes short-term securities.

Largest Holdings [Text Block]

Five largest holdings
Security	Percent of Total Investments^(a)
U.S. Treasury Inflation-Indexed Notes, 2.13%, 04/15/29	5.2	%
U.S. Treasury Inflation-Indexed Notes, 2.38%, 10/15/28	5.0	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/29	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.63%, 10/15/27	4.8	%
U.S. Treasury Inflation-Indexed Notes, 1.25%, 04/15/28	4.7	%

^(a)	Excludes short-term securities.

C000195948 [Member]

Shareholder Report [Line Items]

Fund Name

iShares Municipal Bond Index Fund

Class Name

Institutional Shares

Trading Symbol

BIDIX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about iShares Municipal Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Shares	$25	0.25%

Expenses Paid, Amount

$ 25

Expense Ratio, Percent

0.25%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Institutional Shares returned 1.20%.
For the same period, the ICE BofA US Municipal Securities Index returned 1.58%.

What contributed to performance?

Municipal bonds posted a narrow gain in 2024, with the benefit of income outweighing weakness in prices. For most of the year, municipal bonds performed reasonably well on expectations for interest-rate cuts by the U.S. Federal Reserve (“Fed”). The central bank indeed began its long-awaited interest rate cuts in the autumn, with a half-point reduction in September 2024 and subsequent quarter-point cuts in November and December. However, continued strength in U.S. economic growth, together with concerns about stubborn inflation and hawkish commentary from Fed Chair Jerome Powell following the December meeting, fueled a late sell-off that erased much of the gains achieved in the first 11 months of the year. Municipals outperformed U.S. Treasuries, as strong investor demand and the continued health of state and local government finances caused yield spreads to tighten.

The transportation, tax-backed, and utility sectors delivered the strongest absolute returns in the annual period. In terms of credit tiers, AA rated securities produced the best performance, followed by those rated A and AAA.

What detracted from performance?

Corporate-backed and housing bonds finished with negative absolute returns, as did those in the 8- to 12-year maturity range. No rating class detracted from performance.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: January 1, 2015 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		10 Years
Institutional Shares	1.20	%	0.99	%	2.06	%
ICE BofA US Municipal Securities Index	1.58		1.07		2.33

Performance Inception Date

Nov. 19, 2018

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 233,615,251

Holdings Count | Holding

298

Advisory Fees Paid, Amount

$ 158,610

Investment Company Portfolio Turnover

37.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$233,615,251
Number of Portfolio Holdings	298
Net Investment Advisory Fees	$158,610
Portfolio Turnover Rate	37%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Sector allocation
Sector^(a)	Percent of Total Investments^(b)
Transportation	33.3	%
State	18.4	%
County/City/Special District/School District	14.7	%
Utilities	10.8	%
Corporate	7.4	%
Health	6.6	%
Housing	4.9	%
Education	3.9	%

Credit quality allocation
Credit Rating^(c)	Percent of Total Investments^(b)
AAA/Aaa	10.2	%
AA/Aa	57.3	%
A	25.4	%
BBB/Baa	6.8	%
N/R	0.3	%

^(a)	For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
^(b)	Excludes short-term securities.
^(c)	For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.

Credit Quality Explanation [Text Block]

For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.

Credit Ratings Selection [Text Block]

For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ.

C000195947 [Member]

Shareholder Report [Line Items]

Fund Name

iShares Municipal Bond Index Fund

Class Name

Investor A Shares

Trading Symbol

BIDAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about iShares Municipal Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Investor A Shares	$50	0.50%

Expenses Paid, Amount

$ 50

Expense Ratio, Percent

0.50%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Investor A Shares returned 0.95%.
For the same period, the ICE BofA US Municipal Securities Index returned 1.58%.

What contributed to performance?

What detracted from performance?

Corporate-backed and housing bonds finished with negative absolute returns, as did those in the 8- to 12-year maturity range. No rating class detracted from performance.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: January 1, 2015 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		10 Years
Investor A Shares	0.95	%	0.73	%	1.90	%
ICE BofA US Municipal Securities Index	1.58		1.07		2.33

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 233,615,251

Holdings Count | Holding

298

Advisory Fees Paid, Amount

$ 158,610

Investment Company Portfolio Turnover

37.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$233,615,251
Number of Portfolio Holdings	298
Net Investment Advisory Fees	$158,610
Portfolio Turnover Rate	37%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Sector allocation
Sector^(a)	Percent of Total Investments^(b)
Transportation	33.3	%
State	18.4	%
County/City/Special District/School District	14.7	%
Utilities	10.8	%
Corporate	7.4	%
Health	6.6	%
Housing	4.9	%
Education	3.9	%

Credit quality allocation
Credit Rating^(c)	Percent of Total Investments^(b)
AAA/Aaa	10.2	%
AA/Aa	57.3	%
A	25.4	%
BBB/Baa	6.8	%
N/R	0.3	%

^(a)	For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
^(b)	Excludes short-term securities.
^(c)	For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.

Credit Quality Explanation [Text Block]

Credit Ratings Selection [Text Block]

For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ.

C000201952 [Member]

Shareholder Report [Line Items]

Fund Name

iShares Municipal Bond Index Fund

Class Name

Investor P Shares

Trading Symbol

BIDPX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about iShares Municipal Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Investor P Shares	$50	0.50%

Expenses Paid, Amount

$ 50

Expense Ratio, Percent

0.50%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Investor P Shares returned 0.95%.
For the same period, the ICE BofA US Municipal Securities Index returned 1.58%.

What contributed to performance?

What detracted from performance?

Corporate-backed and housing bonds finished with negative absolute returns, as did those in the 8- to 12-year maturity range. No rating class detracted from performance.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: January 1, 2015 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		10 Years
Investor P Shares	0.95	%	0.74	%	1.90	%
Investor P Shares (with sales charge)	(3.10	)	(0.08	)	1.49
ICE BofA US Municipal Securities Index	1.58		1.07		2.33

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 233,615,251

Holdings Count | Holding

298

Advisory Fees Paid, Amount

$ 158,610

Investment Company Portfolio Turnover

37.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$233,615,251
Number of Portfolio Holdings	298
Net Investment Advisory Fees	$158,610
Portfolio Turnover Rate	37%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Sector allocation
Sector^(a)	Percent of Total Investments^(b)
Transportation	33.3	%
State	18.4	%
County/City/Special District/School District	14.7	%
Utilities	10.8	%
Corporate	7.4	%
Health	6.6	%
Housing	4.9	%
Education	3.9	%

Credit quality allocation
Credit Rating^(c)	Percent of Total Investments^(b)
AAA/Aaa	10.2	%
AA/Aa	57.3	%
A	25.4	%
BBB/Baa	6.8	%
N/R	0.3	%

^(a)	For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
^(b)	Excludes short-term securities.
^(c)	For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.

Credit Quality Explanation [Text Block]

Credit Ratings Selection [Text Block]

For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ.

C000195949 [Member]

Shareholder Report [Line Items]

Fund Name

iShares Municipal Bond Index Fund

Class Name

Class K Shares

Trading Symbol

BIDKX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about iShares Municipal Bond Index Fund (the “Fund”) for the period of January 1, 2024 to December 31, 2024.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.

Additional Information Phone Number

(800) 441‑7762

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last year ?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class K Shares	$20	0.20%

Expenses Paid, Amount

$ 20

Expense Ratio, Percent

0.20%

Factors Affecting Performance [Text Block]

How did the Fund perform last year ?

For the reporting period ended December 31, 2024, the Fund’s Class K Shares returned 1.25%.
For the same period, the ICE BofA US Municipal Securities Index returned 1.58%.

What contributed to performance?

What detracted from performance?

Corporate-backed and housing bonds finished with negative absolute returns, as did those in the 8- to 12-year maturity range. No rating class detracted from performance.

Performance Past Does Not Indicate Future [Text]

Past performance is not an indication of future results.

Line Graph [Table Text Block]

Fund performance

Cumulative performance: January 1, 2015 through December 31, 2024

Initial investment of $10,000

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns
	1 Year		5 Years		10 Years
Class K Shares	1.25	%	1.03	%	2.09	%
ICE BofA US Municipal Securities Index	1.58		1.07		2.33

Performance Inception Date

Nov. 19, 2018

No Deduction of Taxes [Text Block]

Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.

Updated Performance Information Location [Text Block]

Visit blackrock.com for more recent performance information.

Net Assets

$ 233,615,251

Holdings Count | Holding

298

Advisory Fees Paid, Amount

$ 158,610

Investment Company Portfolio Turnover

37.00%

Additional Fund Statistics [Text Block]

Key Fund statistics
Net Assets	$233,615,251
Number of Portfolio Holdings	298
Net Investment Advisory Fees	$158,610
Portfolio Turnover Rate	37%

Holdings [Text Block]

What did the Fund invest in?

(as of December 31, 2024)

Sector allocation
Sector^(a)	Percent of Total Investments^(b)
Transportation	33.3	%
State	18.4	%
County/City/Special District/School District	14.7	%
Utilities	10.8	%
Corporate	7.4	%
Health	6.6	%
Housing	4.9	%
Education	3.9	%

Credit quality allocation
Credit Rating^(c)	Percent of Total Investments^(b)
AAA/Aaa	10.2	%
AA/Aa	57.3	%
A	25.4	%
BBB/Baa	6.8	%
N/R	0.3	%

^(a)	For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
^(b)	Excludes short-term securities.
^(c)	For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.

Credit Quality Explanation [Text Block]

Credit Ratings Selection [Text Block]

For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ.